1. Field of the Invention
This invention relates in general to semiconductor devices and, more particularly, to a semiconductor device assembly having a heat-dissipating lead-frame.
2. Description of the Related Art
As used herein, the term xe2x80x9csemiconductor chipxe2x80x9d refers to a silicon chip or die containing circuitry to form an active device. The term xe2x80x9csemiconductor device assemblyxe2x80x9d refers to the semiconductor chip, associated components and packaging. The associated components include a lead-frame for mechanically and electrically connecting the device, and internal connections from the chip to the lead-frame. Efforts to provide better semiconductor device assemblies have targeted improving the associated components and packaging.
FIGS. 1 and 2A illustrate a device assembly 5 that uses a plastic package 9 to encapsulate a semiconductor chip 7. FIG. 2A is a cross-sectional view of the semiconductor device assembly 5 along line Bxe2x80x94B of FIG. 1. The plastic housing 9 is a rectangular parallelepiped having length a, width b, and height c. The width b is often relatively small compared to a and c. The device assembly 5 also includes a lead-frame 19 comprising a paddle 10, electrical lead terminals 13, and support legs 17. The terminals 13 transmit input and output signals between the chip 7 and a circuit board (not shown). Metallic wires 15 electrically couple electrode contacts 11 on the chip 7 to the lead terminals 13. The support legs 17 provide means for vertically mounting the device assembly 5 on a circuit board.
FIG. 2B illustrates the mechanical attachment of the prior art paddle 10 to the semiconductor chip 7. Since the semiconductor chip 7 is a thin and fragile structure, the paddle 10 provides needed mechanical support to protect the semiconductor chip 7 from damage during handling, attachment to the lead terminals 13, and packaging. Typically the paddle 10 is mechanically attached to the semiconductor chip 7 prior to handling and electrical attachment. Since the purpose of the paddle 10 is to give mechanical protection to the semiconductor chip 7, the area of the paddle 10 is generally substantially equal to the area of the semiconductor chip 7. The package 9 encapsulates both the paddle 10 and the semiconductor chip 7 in an insulating material, e.g., plastic.
Referring to FIG. 2A, prior art manufacturing techniques produce the entire lead-frame 19; i.e., the paddle 10, the lead terminals 13, and the support legs 17; from the same material. The lead-frame 19 is often made of a metal alloy or copper and may be produced by stamping or etching the components out of a single piece of metal.
Referring to FIGS. 1 and 2A, the prior art lead-frame 19 provides very limited heat dissipation, because the lead frame 19 is substantially encapsulated within the thermally insulating package 9. Though the electrical terminals 13 and support legs 17 are exposed to the exterior, these components do not have a good thermal contact with the heat producing chip 7 and do not have sufficient external surface area to provide substantial thermal cooling to the chip 7. Thus, the device assembly 5 does not provide the substantial cooling needed for high power chips (not shown).
Heat dissipation must be considered in designing packaging for high power semiconductor chips, because the heat produced may damage the chip if not efficiently dissipated. Plastic packaging substantially impedes heat dissipation due to plastic""s insulating properties. High power chips such as static and dynamic random-access memories (xe2x80x9cSRAMxe2x80x9d and xe2x80x9cDRAM,xe2x80x9d respectfully), transistor-transistor logic (xe2x80x9cTTLxe2x80x9d) and Sync-Link DRAM (xe2x80x9cSLDRAMxe2x80x9d) can produce substantial heat, e.g., up to 2 watts in chips such as SLDRAMs.
Some prior art devices add a heat sink (not shown) to the device assembly 5 of FIGS. 1 and 2A to provide additional cooling for the semiconductor chip 7. The heat sink must be thermally coupled to the semiconductor chip 7 to provide adequate cooling. Thus, an additional fabrication step is needed to couple the heat sink to the chip 7. The additional step can add time and cost to the manufacture of the semiconductor device assembly.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In a first aspect of the present invention, a semiconductor device assembly is provided. The semiconductor device assembly includes a heat-dissipating lead-frame, a semiconductor chip coupled to the heat-dissipating lead-frame, and an insulating package encapsulating the semiconductor chip and an internal portion of the heat-dissipating lead-frame. The heat-dissipating lead-frame is constructed of a single material.
In a second aspect of the present invention, a process is provided for fabricating a semiconductor device assembly. The process includes providing a lead-frame that includes a paddle with external and internal portions, providing a semiconductor chip, thermally coupling the semiconductor chip to the internal portion. The process also includes encapsulating the semiconductor chip and the internal portion in an insulating material.